Conventionally, as a method of joining a pipe and another member, for example, the following method is used.
A pipe is inserted into an insertion hole formed in another member and an expansion die having a wedge hole portion and circumferentially divided centering on the wedge hole portion into a plurality of segments is disposed in the hollow portion of the pipe. Next, the wedge portion of the mandrel is inserted into the wedge hole portion of the die to thereby move each segment of the die in the radially outward direction of the pipe. With this, the inserted portion of the pipe inserted into the insertion hole and the portions axially adjacent to the inserted portion are pushed outwardly by the die segments to execute the expansion work (tube diameter expansion work) to thereby join another member to the pipe. (see, e.g., Patent Documents 1 and 2). This method is called a ridge lock method.
Although it is not a joining method for members, as an expansion method for a circular cylindrical member using a die, there is known a method described in Japanese Unexamined Laid-open Patent Publication No. 2002-224743, for example. (see, Patent Document 3).    Patent Document 1: Japanese Unexamined Laid-open Patent Publication No. H4-8818 (page 2, FIG. 8)    Patent Document 2: Japanese Unexamined Laid-open Patent Publication No. H11-36859    Patent Document 3: Japanese Unexamined Laid-open Patent Publication No. 2002-224743